Robert Wood, the US deputy ambassador to the UN, told the Security Council that Russia could have improved its human rights record since its suspension in April 2022.
“Russia's own actions make it unfit to serve on the Human Rights Council,” Mr Wood said.
“What further evidence does the international community need? The massive death toll in Ukraine rises every day. New unspeakable horrors are discovered.”
Moscow is attempting to rejoin the Geneva-based body in defiance of western nations' attempts to isolate it over the invasion.
The vote is scheduled for Tuesday in the 193-member General Assembly.
Last week, the village of Hroza in eastern Ukraine suffered one of the deadliest attacks on civilians since the war began, wiping out about one in six of its population.
The Russian missile strike reduced a village cafe and shop to rubble, killing at least 52 people.
The UN said it had documented nearly 10,000 civilian deaths since the start of the invasion in February 2022 but pointed out the actual number was far higher.
Ukraine’s UN ambassador Sergiy Kyslytsya, who voiced profound apprehension regarding Russia's candidacy, warned “any vote in favour of ... candidacy will be a bullet in the UN body”.
“We believe in the wisdom and moral integrity of the UN community to prevent this from happening."
Albania's UN ambassador Ferit Hoxha said the UN General Assembly "has an important choice" to "demonstrate that it is not ready to take an arsonist for a firefighter."
In its paper circulated to the UN last week, Russia said it elected, it would use its membership to prevent the “increasing trend” of turning the Human Rights Council into an “instrument which serves the political will of one group of countries punishing non-loyal governments for their independent and external policy”.